A method, system, and program product are provided for updating software deployed on computers in an enterprise computer network wherein each computer has a software update agent installed to enable the computer to receive software patch updates. The method includes determining a required software component and updates based upon a location in a configuration file; determining a version of the agent and updating the agent if required; selecting a server from which required updates are to be downloaded; scanning a plurality of software components on a selected computer and comparing the components with updates available on the server to determine required updates; downloading the required patches from the server; and installing the patches on the selected computer. The system includes components that perform the method steps when operated on a computer in the network. A computer readable medium implements the method for updating software deployed on computers in a network.

Claim:

What is claimed is:

1. A method, comprising: determining, by a computer comprising a processor and memory, a required software component and software patch update based upon a location set in aconfiguration file; executing, by the computer, at least one command-line switch which identifies a location of the configuration file and wherein all subsequent software component and software patch update settings are provided from the configurationfile, wherein the configuration file is located in a same folder as a patch update processor executable file, wherein the command-line switch overrides settings in the configuration file.

2. The method of claim 1 comprising determining, by the computer, a version of a software update agent and updating the software update agent if required, wherein the step of updating the software update agent is based on a minimum version ofthe software update agent, an update location, and a command-line set in the configuration file.

3. The method of claim 1 further comprising adding or removing a server update service setting based on the command-line switch or the configuration file.

4. The method of claim 1 further comprising selecting a server from which required software patch updates are to be downloaded, wherein the step of selecting a server comprises determining a server update service setting in the configurationfile.

5. The method of claim 4 further comprising selecting a server update service server if the server update service setting is set.

6. The method of claim 4 further comprising selecting a software update server if the server update service setting is not set.

7. The method of claim 5 wherein the server update service server is located within an enterprise firewall.

8. The method of claim 6 wherein the software update server is located on a software provider's website.

9. The method of claim 1 further comprising downloading the required software patch update from a software provider's website to a server update service server on a periodic basis.

10. The method of claim 1 further comprising logging all operations performed during the software patch update process in a log file.

11. The method of claim 1 further comprising versioning of the software patch update using the configuration file.

12. The method of claim 3 wherein adding or removing a server update service setting is performed using a configuration file registry.

13. The method of claim 1 further comprising rebooting of the computer if required for the software patches to become operational.

14. A system, comprising: a processor; a memory, wherein the processor and the memory are communicably coupled to each other; and an application that, when executed by the processor, executes at least one command-line switch which identifiesa location of a configuration file and wherein all subsequent software component and software patch update settings are provided from the configuration file, wherein the configuration file is located in a same folder as a patch update processorexecutable file, wherein the command-line switch overrides settings in the configuration file.

15. The system claim 14 wherein the system determines a minimum version of a software update agent and an update location from which an updated version of the software agent can be downloaded.

16. The system of claim 14 wherein the system adds or removes a server update service setting based on the command-line switch.

17. The system of claim 14 wherein the system determines a server update service setting in the configuration file.

18. The system of claim 17 wherein the system selects a service update service server if the server update service setting is set.

19. The system of claim 17 wherein the system selects a software update server if the server update service setting is not set.

20. The system of claim 18 wherein the server update service server is located within an enterprise firewall.

21. The system of claim 19 wherein the software update server is located on a software provider's website.

22. The system of claim 14 wherein the system downloads required software patch updates from a software provider's website to a server update service server on a periodic basis.

23. The system of claim 14 wherein the system logs all operations performed during the software patch update process in a log file.

24. The system of claim 14 wherein a system versioning of software update patches is based on the configuration file.

25. The system of claim 16 wherein the system uses a configuration file registry to add or remove a server update service setting.

26. The system of claim 14 wherein the system reboots the selected computer if required for software patches to become operational.

27. A non-transitory computer readable storage medium comprising instructions for: determining a required software component and software patch update based upon a location set in a configuration file; executing, by the computer, at least onecommand-line switch which identifies a location of the configuration file and wherein all subsequent software component and software patch update settings are provided from the configuration file, wherein the configuration file is located in a samefolder as a patch update processor executable file, wherein the command-line switch overrides settings in the configuration file.

28. The non-transitory computer readable storage medium of claim 27 comprising instructions for updating a software agent by determining a minimum version of the software update agent and an update location from which an updated version of thesoftware agent can be downloaded.

29. The non-transitory computer readable storage medium of claim 27 comprising instructions for adding or removing a server update service setting based on the command-line switch or the configuration file.

30. The non-transitory computer readable storage medium of claim 27 comprising instructions for electing a server by determining a server update service setting in the configuration file.

32. The non-transitory computer readable storage medium of claim 30 comprising instructions for selecting a software update server if the server update service setting is not set.

33. The non-transitory computer readable storage medium of claim 27 comprising instructions for downloading a required software patch update from a software provider's website to a server update service server on a periodic basis.

34. The non-transitory computer readable storage medium of claim 27 comprising instructions for logging all operations performed during the software patch update process in a log file.

36. The non-transitory computer readable storage medium of claim 27 comprising instructions for adding or removing a server update service setting is performed using a configuration file registry.

Description:

BACKGROUND OF THE INVENTION

The present invention relates generally to maintaining computer software deployed in a corporate enterprise's information processing systems and, more particularly, to methods and systems for managing security patch updates to the softwareinstalled on the servers and workstations of a corporate enterprise.

Most security incidents with computers today are caused by flaws in software referred to as vulnerabilities. The ultimate solution to software vulnerabilities is application of patches. Software vendors generally release patches to fixvulnerabilities in their software products. If applied correctly, patches remove vulnerabilities from computer systems.

An important problem is to determine how often to update the computer systems in the corporate enterprise with the necessary patches. There are many factors that go into determining when patches should be applied. One factor is the number ofvulnerabilities to patch. Sorting through all the vulnerabilities to find the relevant vulnerabilities to patch can be tedious and labor-intensive. Before being applied in a production environment, each patch must be tested to ensure that it worksproperly and does not interfere with existing applications installed on a computer system. In addition, every patch requires installation after testing. If a patch is applied to a critical system, downtime can be very costly.

Although it used to be a common practice among software vendors to release patches as soon as they were available, the common practice today is to release patches on a monthly basis. For example, Microsoft Corporation switched to a monthlypatch release cycle in October 2003. "Patch Tuesday" is the second Tuesday of each month and is the day on which Microsoft releases security patches.

In large corporations, keeping thousands of computers up-to-date with security patches requires a great deal of Information Technology (IT) department manpower every month to update the servers and workstations with the latest released patches. This results in numerous people writing different scripts customized to each set of patches. The login script then checks every workstation and applies the patches. Other scripts are used to manually update servers either because they are missed byMicrosoft's Systems Management Software or for new server builds, and are applied to machines that access the corporation's network from an Internet Remote Access Service (IRAS). More scripts are written to apply to new workstations that are beingbuilt.

There is a need in the art for improved techniques for managing security patch updates to software installed on the servers and workstations of a large enterprise to significantly reduce the amount of monthly work required to maintain backupprocess scripts. There is a further need for a method that enables the timing of the download and installation of security patch updates, and computer reboot, if necessary, to be under direct control of a system administrator.

SUMMARY OF THE INVENTION

Embodiments of the invention are directed to methods and systems for managing security patch updates to software installed on the servers and workstations of a large enterprise. In one embodiment, the security patch update processor is a toolfor inspecting personal computers and servers running Microsoft Windows.RTM. operating system software for required security patches and patching the software if required. It has been designed to be secure, adaptable and modular, making it easy toupdate and modify. The security patch update processor of the present invention is completely configurable using command line switches and/or a configuration file.

In one aspect of the invention, a method, system, and program product are provided for updating software deployed on a plurality of computers in an enterprise computer network wherein each computer has a software update agent installed to enablethe computer to receive software patch updates. The method includes determining a required software component and software patch updates based upon a location set in a configuration file; determining a version of the software update agent and updatingthe software update agent if required; selecting a server from which required software patch updates are to be downloaded; scanning a plurality of software components on a selected computer and comparing the software components with software patchupdates available on the selected server to determine required software patch updates; downloading the required software patches from the selected server; and installing the required software patches on the selected computer. The system includes aplurality of components that perform the steps of the method when operated on a computer in the network. The computer readable medium implements the method for updating software deployed on a plurality of computers in an enterprise network.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages and aspects of the present invention will become apparent and more readily appreciated from the following detailed description of the invention taken in conjunction with the accompanying drawings, as follows.

FIG. 1 illustrates a prior art single server scenario for distributing updates to client computers in a simple computer network using a Microsoft Windows Server Update Services (WSUS) server. This is the server component that is installed on acomputer running a Windows Server 2003 operating system inside the corporate enterprise firewall.

FIG. 2 illustrates an exemplary help screen for the security patch update processor that is accessible to the enterprise system administrator.

FIG. 3 illustrates processing logic for the security patch update processor in accordance with an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description of the invention is provided as an enabling teaching of the invention and its best, currently known embodiment. Those skilled in the relevant art will recognize that many changes can be made to the embodimentsdescribed, while still obtaining the beneficial results of the present invention. It will also be apparent that some of the desired benefits of the present invention can be obtained by selecting some of the features of the present invention withoututilizing other features. Accordingly, those who work in the art will recognize that many modifications and adaptations to the present invention are possible and may even be desirable in certain circumstances, and are a part of the present invention. Thus, the following description is provided as illustrative of the principles of the present invention and not in limitation thereof, since the scope of the present invention is defined by the claims.

Embodiments of the invention significantly reduce the amount of monthly work required to maintain backup process scripts. The invention will be described herein in the context of a corporate enterprise environment in which Microsoft server andclient products are installed on the host computer systems, servers, workstations, and laptops of the corporate enterprise. However, the inventive concepts described herein are applicable to other operating system environments including Linux, and otherapplication software products that regularly issue security patches over the Internet. For an installed base of Microsoft software products, the invention makes use of the Microsoft Windows Server Update Services (WSUS) server. An enterprise can allowthe WSUS server to maintain communication with Microsoft, which automatically downloads all released patches to the WSUS server. Each month, an enterprise representative (e.g., system administrator) approves patches that have been determined asacceptable by the enterprise and that should be installed on its machines.

The security patch update processor removes the need to have individual custom scripts created every month to handle the different security updates. Furthermore, the security patch update processor makes use of the internal Windows updateservice to allow each machine to perform a self-evaluation in conjunction with settings on the centralized WSUS server. The security patch update processor allows an enterprise to more closely manage when the Windows update process takes place usingscripts. The security patch update processor is designed to be configurable and flexible to apply to different environments and needs. The Windows Server Update Services software is downloaded and installed on an enterprise server. Windows ServerUpdate Services software maintains itself by automatically downloading all released software updates.

The enterprise system administrator selects and approves the security updates to install on its machines. The security patch update processor sets the machines it runs on to get updates from the WSUS, then scans the machine for its requirementsusing the Windows Server Update Service, and optionally downloads and installs the required updates from the WSUS. The security patch update processor enables immediate updates to the machine it runs on providing an advantage over prior art processesfor installing patches. This is especially important when enterprise policy requires that all affected machines be patched with updates within a set period of time. The security patch update processor also can be configured to automatically reboot,prompt for reboot or suppress reboot according to the needs of the machine type. The security patch update processor can take a large number of command-line settings, or can optionally use a configuration file to pass command-line arguments. Insummary, the security patch update processor provides the ability to scan, download, and install patches which are enterprise-managed on a WSUS.

In an exemplary embodiment of the present invention, the security patch update processor performs the following process steps: 1. Checks for required components and updates for these components based upon the location set in the configurationfile. 2. Checks the version of Microsoft Windows Update Agent.RTM. (WUA) and updates according to minimum version, update location and command-line set in the configuration file. 3. Sets or removes Windows Server Update Service.RTM. (WSUS) settingsaccording to command-line switches or configuration file. 4. Scans computer for required security patches. If WSUS settings are set, this scan takes place against the managed WSUS server. Otherwise the scan takes place against the Microsoft WindowsUpdate site. 5. Downloads patches determined to be required for the specific machine by the scan. If WSUS settings are set, this download comes from the managed WSUS server. Otherwise the download comes from the Microsoft Windows Update site. 6. Installs patches previously downloaded as a result of the scan. 7. Allows for versioning of the patching process by using the configuration file. 8. All process steps are prompted by default, although command-line switches can set prompting to"silent," "suppress reboots" or "prompt for reboots only." These settings can also be applied via the configuration file. 9. The configuration file, named pup.cfg, can be located in the same folder as the patch update processor executable file, pup.exe(default setting), in which case command-line switches override settings in the configuration file. The location of the configuration file can be passed via the command-line switch. In this case, it is the only command-line switch that is recognized. All other settings will come from the configuration file. 10. Using the configuration file registry, settings can be added or removed. 11. All operations performed by the security patch update processor are logged by default to a log file located inthe same folder location as pup.exe, named pup.log. The log file location and name can be changed to any other location using either the command-line switches or in the configuration file. If the configuration file is used, the name of the file can berepresented by the name of the machine creating the file.

The security patch update processor can be configured in two different ways. Settings can be passed either using the command-line or a configuration file. While most settings can be set on the command-line, there are more settings availableusing the configuration file. The administrator screen illustrated in FIG. 2 can be displayed using the -h switch. If the -h switch is used, all other switches are ignored.

Even though the administrator screen indicates that not passing arguments will perform the same way as a -v switch (i.e., returns the version of WUA), this behavior is modified when a configuration file (pup.cfg) is present in the same folderlocation of the executable file (pup.exe). In this scenario, passing no arguments will cause execution to use the settings in the configuration file.

Security Patch Update Processor Command-Line Switches

The command-line switches come in three different sets. The first set, or process set, determines which process execution will follow. The -v switch will simply show the version of the Windows Update Agent which will also be shown during allother processes. The main processes, however, scan, download, and install build upon each other. So, only one process switch is needed at a time. The second set of switches amends how the process switch is run in regard to prompting. Only one ofthese switches is used at a time. In the absence of a prompting, switch execution will prompt at every step during the selected process (when not overridden by the configuration file). The third set of switches can all be used at the same time, withthe exception of the -h switch (help screen).

The following scenarios show how the different switches can be used. In these examples, the assumption is that there is not a configuration file unless specified on the command-line.

Pup -s

This example is the most basic command and will cause the machine to simply scan and report which patches are needed. If the WSUS settings are not set, then it will use the Microsoft Update Internet site, otherwise it will use WSUS.

Pup -d

This is another example of the most basic command and will cause the machine to simply scan, report which patches are needed and download those patches to the machine in preparation of install. If the WSUS settings are not set, then it will usethe Microsoft Update Internet site, otherwise it will use WSUS. There will be no prompting for a simple scan.

Pup -i

This is another example of the most basic command and will cause the machine to scan, report which patches are needed, download those patches to the machine in preparation of install, and install them. If the WSUS settings are not set, then itwill use the Microsoft Update Internet site, otherwise it will use WSUS. Since there is not a prompting switch, there will be a prompt to allow downloading to continue.

Pup -whttp://wsus.enterprise.com -i

This example shows how to set the WSUS. Note that the WSUS will only be set the first time. The -w switch will be ignored after that unless the setting changes. Since there is not a prompting switch, every step will be prompted except for thescan. Prompts will precede the download and install steps, and if a reboot is required a message box will appear giving the option to reboot or not.

Pup -w -i

This example shows how to remove the WSUS setting. Note that the WSUS removal will only be set the first time. The -w switch will be ignored after that unless the setting changes.

Pup -whttp://wsus.enterprise.com -ld:\logs\pup.log -i -r

This example uses the WSUS setting for the install, redirects the log file, instructs execution to scan, download and install the patches, and then prompts if a reboot is required. Otherwise there will be no other prompting.

Pup -whttp://wsus.enterprise.com -ld:\logs \pup.log -i -q

This is the exact same configuration as in the preceding example, except with a -q switch that suppresses all prompts, including the reboot prompt. With this setting, if a reboot is required, the machine will reboot automatically as soon as allof the installs are complete. If a reboot is not required, the process will complete and simply come to an end.

Pup -whttp://wsus.enterprise.com -ld:\logs\pup.log -i -n

This is the exact same configuration as in the two preceding examples, except with a -n switch that suppresses all prompts and all reboots as well. With this setting, if a reboot is required, the machine will not reboot. The process willcomplete and simply come to an end.

Pup -c\\fileserver1\patches\patch.cfg

This example shows how to redirect all of the settings to a configuration file.

Security Patch Update Processor Configuration File

The configuration file is laid out in the same format as an initialization (ini) file. Each section is named using a string enclosed within squared brackets "[ ]". Each value is given a string name followed by an equal sign ("="), then astring value is assigned to the name. The exception to this is the registry settings section. This section is enumerated according to the number of registry settings required to be set or removed.

If a file named pup.cfg exists in the same folder as pup.exe it will be used by default, unless another path is passed with the -c switch at the command-line. If the default configuration file is used, the settings in it can be overridden withcommand-line switches. If the -c switch is used on the command-line with a viable path to a configuration file, all other command-line switches and all settings in the local configuration file will be ignored.

Security Patch Update Processor Configuration Section

[Patch Version]--This section defines the versioning of the patching process. If set to be used by setting UseVersion to true, security patch update processor will set the registry key and values established by VersionReg and Version Val,respectively, to the value placed in Version when it has successfully scanned and updated the machine, if required. On subsequent runs, security patch update processor will exit immediately after launch if the registry setting is greater than or equalto the version set in the configuration file.

Version--Numeric version which will be set in the registry and compared on subsequent passes.

VersionReg--Registry key location where version value will be set.

VersionVal--Registry value where version will be stored.

[WSUS]--This section determines whether WUA will use WSUS or Windows Update Internet site to get its scan information and download patch files.

SetWSUS--Boolean (true or false) which establishes if WSUS is to be used. WSUS can be set at the command-line with the -w switch or it can be set in the configuration file (SetWSUS=true). If the configuration file is local, the command-linewill override the configuration file. If the configuration file is set at the command-line, the configuration file settings will override any other switches set at the command-line. If this setting is set to false, it will not remove the WSUS settings. It will only stop any setting from being set according to the event process above. WSUS settings are set or removed only by using the -w command-line switch or the true statement in the setting in the configuration file. To remove WSUS settings usingthe configuration file, this value is set to true and the other values under the [WSUS] section are removed and either no other switches are used (if local configuration file is used), or the -c switch is used to pass the location of the configurationfile.

WSUServer/StatusServer--When set at the command-line, both the WSUServer and the StatusServer settings are set to the same thing, whatever is passed to the -w switch. The configuration file offers an opportunity to have them set differently, ifdesired.

WSUSRegPath--The default registry setting for WSUS settings is HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate. The configuration file allows for an alternative location. This should not be changed in the configuration file unless thelocation actually changes as the setting in the configuration file overrides what is internally set in the program. The same thing is true for the rest of the settings under WSUS. They are there for the purpose of revising the default settings ofMicrosoft Windows Update in case they change and should not be modified except in this case.

[WSUSRegAdds]--This section allows for other registry settings for WSUS to be set which cannot be set by the command-line. An HKEY is a handle to the Windows registry key. The format should be exactly like in the example shown above in thatthe registry root should use the three or four letter representation: HKLM=HKEY_LOCAL_MACHINE HKCU=HKEY_CURRENT_USER HKCR=HKEY_CLASSES_ROOT HKCC=HKEY_CURRENT_CONFIG HKU=HKEY_USERS

The HKEY is followed by a backslash with the full path to the registry key. This is followed again by a backslash and the value name which is followed by an equal sign (=) and then the value.

String Values--If the value is a string or REG_SZ then the value alone is fine. If the value has percent signs (%) in the string it will automatically be converted to an expanded string or REG_EXPAND_SZ.

[ADHocRegAdds] and [ADHocRegDels]--Provides a way to add or remove other registry settings outside of the WSUS settings. The format is exactly the same as the WSUS registry settings above.

[Parameters]--This section provides the operational direction of program execution.

The first three values, Scan, Download and Install replace the -s, -d and -i switches at the command-line. It is important to note that each command is dependent on the previous command. In other words, the Install command requires that thedownloads have taken place which depends on the scan having taken place. So the commands must be used from scan down. All three can be true. Scan and download can be true and install false. Scan only can be true while download and install are false. This is similar to the command-line switches in this way.

Prompt--Sets the prompt level by numeric code as shown in Table 1:

TABLE-US-00001 TABLE 1 Numeric Code Meaning Explanation 0 prompt all this level corresponds to no prompt switches on the command-line. 1 reboots only this level corresponds to the -r switch on the command-line. 2 suppress reboots and thislevel corresponds to the -n prompts command-line switch. 3 no prompts (not even this level corresponds to the -q (silent) for reboots) switch.

Loglocation--This is used to redirect the location of the log file.

Logfilename--The name of the log file. The file name can be substituted with @ComputerName@ variable to cause the program to substitute the machine name for the log file name.

[WindowsUpdate]--This section is used to replace default program settings if necessary. In most cases these settings should not be changed. The exception is the WUAMinVersion, UpdateWUA and WUAUpdateCmd. These three settings allow for theability to update the Windows Update Agent if available and needed.

The current setting of WUAMinVersion is the minimum WUA version required for the security patch update processor to be able to work with WUA. The security patch update processor will automatically detect the file version of the file representedby WUAEngDll. If it is less than the value in WUAMinVersion it will determine if there is a value in WUAUpdateCmd. If there is, it will attempt to run the update. If it is successful, it will continue. If it is not, it will exit.

The format of WUAUpdateCmd requires the full path to the update executable followed by a semicolon (;) and then a parameter, as in/quiet.

The security patch update processor requires the file Interop.WUApiLib.dll in order to make use of WUA system calls. Before it attempts to perform any of these calls it checks to see if the file is located in the same path as the executable. If it does not find the file it exists. However, if there is a value in WUAPIUpdatePath pointing to a file represented in WUAPIDll, it will attempt to copy the file local. If it is successful, it will continue. If not, it will exit.

FIG. 3 illustrates exemplary processing logic for the security update patch processor. The patch update processor allows for versioning of the patching process using the configuration file. All steps in the process are prompted by default,although command-line switches can set prompting to silent, suppress reboots, or prompt for reboots only. These settings also can be applied via the configuration file.

The configuration file, named pup.cfg, can be located in the same folder as pup.exe (default setting), in which case command line switches override settings in the configuration file. Registry settings can be added or removed using theconfiguration file.

All operations performed by the patch update processor are logged by default to a log file located in the same folder location as pup.exe, named pup.log. The log file location and name can be changed to any other location using either thecommand-line switches or in the configuration file. If the configuration file is used, the name of the file can be represented by the name of the machine creating the file.

The processing logic begins with the patch update processor checking for required components and updates based upon the location set in the configuration file, as indicated in logic block 300. The patch update processor checks for the versionof the Microsoft Windows Update Agent (WUA), and updates according to the minimum version, update location, and command line set in the configuration file, as indicated in logic block 304. The patch update processor then sets or removes the WindowsServer Update Service (WSUS) settings according to command-line switches or the configuration file, as indicated in logic block 308.

The patch update processor scans the computer for required security patches as shown in logic block 312. If the patch update processor determines that WSUS settings are set in decision block 316 (e.g., SetWSUS=true), the scan for requiredsecurity patches takes place against the managed WSUS server as indicated in logic block 320. Otherwise, the scan takes place against the Microsoft Windows Update site as indicated in logic block 324. Next, as indicated in logic block 328, the patchesthat are determined to be required for the specific machine are downloaded from the managed WSUS server or Microsoft Windows Update site, as appropriate. If WSUS settings are set, the patch download comes from the managed WSUS server, as indicated inlogic block 332. If WSUS settings are removed, the patch download comes from the Microsoft Windows Update site, as indicated in logic block 336. Patches are then installed on the machine as indicated in logic block 340. The patch update processor logsall patch update operations performed to a log file as indicated in logic block 344. The process ends in block 350.

The system and method of the present invention have been described as computer-implemented processes. It is important to note, however, that those skilled in the art will appreciate that the mechanisms of the present invention are capable ofbeing distributed as a program product in a variety of forms, and that the present invention applies regardless of the particular type of signal bearing media utilized to carry out the distribution. Examples of signal bearing media include, withoutlimitation, recordable-type media such as diskettes or CD ROMs, and transmission type media such as analog or digital communications links.

The corresponding structures, materials, acts, and equivalents of all means plus function elements in any claims below are intended to include any structure, material, or acts for performing the function in combination with other claim elementsas specifically claimed.

Those skilled in the art will appreciate that many modifications to the exemplary embodiment are possible without departing from the scope of the present invention. In addition, it is possible to use some of the features of the presentinvention without the corresponding use of the other features. Accordingly, the foregoing description of the exemplary embodiment is provided for the purpose of illustrating the principles of the present invention, and not in limitation thereof, sincethe scope of the present invention is defined solely by the appended claims.